We have developed in vivo EEM system which can collect 10 fluorescence spectra excited with 10 different light sources and diffuse reflectance spectra from the same tissue in less than a second. This system is currently being used to study precancerous changes in Barrett's esophagus and colon. So far we have examined nearly 55 patients undergoing surveillance for dysplasia in Barrett's esophagus. The system is also being used at the Brigham and Women's Hospital for studying adenomatous polyps and dysplasia in colon. The wealth of fluorescence information provided by rapid EEM system is being analyzed using model based approach and principal component analysis approach.